Constant velocity joints have been known as components for transmitting the torque of a drive shaft of an automobile to an axle of the automobile.
Since constant velocity joints allow the angular displacement between a driving shaft and a driven shaft while keeping the speed of the driving and driven shafts constant, they are being used not only in automobiles but also in various industrial machines, home appliances, office machines, etc.
There are two types of constant-velocity joints, namely, fixed constant-velocity joints, which only permits an angular displacement, and sliding constant-velocity joints, which permit both angular and axial displacements. Japanese Unexamined Patent Application Publication No. 2007-255511 discloses a sliding constant-velocity joint.
The constant-velocity joint disclosed in JP 2007-255511 is called “tripod-type constant velocity joint”, and includes an outer ring on the inner periphery thereof, the outer ring being formed with three axially extending track grooves which are circumferentially arranged at intervals of 120 degrees. A tripod member is mounted inside of the outer ring, and formed with three radial protrusions (leg shafts) slidably inserted in the respective track grooves, so that torque is transmitted between the outer ring and the tripod member.
The outer ring has bulges between the respective adjacent track grooves. Each of the bulges is formed at its distal end with a pair of tapered surfaces inclined in circumferentially opposite directions to each other so as to define an apex at the center of the bulge with respect to its circumferential width. Each of the protrusions is formed at its front portion with a pair of tapered surfaces inclined from the widthwise center of the protrusion toward both sides thereof so as to define an apex at the widthwise center of the protrusion, so that the tripod member can be easily inserted into and separated from the outer ring.
The tripod-type constant velocity joint disclosed in JP 2007-255511 is advantageous in that the tripod member can be easily inserted into and separated from the outer ring, no grease lubrication is necessary, it is lightweight and small in size, and it generates less noise.
Generally, in various kinds of devices in which a constant velocity joint is used, for maintenance or exchange of components due to their deterioration, in some cases, a driving shaft and a driven shaft are repeatedly connected to the joint (such that driving force is transmitted) and separated from the joint (such that driving force is not transmitted). Therefore, the tripod-type constant velocity joint of JP 2007-255511 is configured as described above, so that the tripod member can be easily inserted into and separated from the outer ring.
The constant-velocity joint of JP 2007-255511 allows the center axis of the driving shaft and the center axis of the driven shaft to be inclined relative to each other with a relatively large angle therebetween, provided that the two center axes intersect with each other in or near the joint.
However, this constant-velocity joint does not allow the above two center axes to be inclined relative to each other with a relatively large angle, if the above two center axes intersect with each other at a position remote from the joint. Also, this constant-velocity joint does not allow a large offset between the above two center axes if the center axes are parallel to each other.
In the tripod-type constant-velocity joint of JP 2007-255511, when the tripod member is inserted into the outer ring from its open side, even if the track grooves are circumferentially displaced from the respective protrusions, the protrusions are guided by the tapered surfaces formed at the distal ends of the bulges, while kept contact with the tapered surfaces, to the openings of the track grooves at their distal ends. This eliminates the necessity to align the track grooves with the respective protrusions, thus making the connection of the tripod-type constant velocity joint extremely easy.
However, the connection of the joint cannot be smoothly performed in rare cases. At this time, if this connection is forcibly performed, the apexes of the bulges and the apexes of the protrusions might be damaged.
After investigating the cause of such a problem, it turned out that when the connection of the joint is performed, the apexes of the bulges are completely aligned with the respective apexes of the protrusions, namely “three-point support” arises in a stable state, so that the tripod member is not guided by the tapered surfaces of the outer ring. Moreover, it turned out that if the tripod member is forcibly pushed into the outer ring in the above state, a pushing force larger than expected is applied thereto, so that the above apexes kept in contact with each other might be damaged.